Auxin-treatment induces recovery of phytoplasma-infected periwinkle

Aims: To test the effect of auxin-treatment on plant pathogenic phytoplasmas and phytoplasma-infected host. Methods and Results: In vitro grown periwinkle shoots infected with different ‘ Candidatus Phytoplasma’ species were treated with indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA). Both auxins induced recovery of phytoplasma-infected periwinkle shoots, but IBA was more effective. The time period and concentration of the auxin needed to induce recovery was dependent on the ‘ Candidatus Phytoplasma’ species and the type of auxin. Two ‘ Candidatus Phytoplasma’ species, ‘ Ca. P. pruni’ (strain KVI, clover phyllody from Italy) and ‘ Ca. P. asteris’ (strain HYDB, hydrangea phyllody), were susceptible to auxin-treatment and undetected by nested PCR or detected only in the second nested PCR in the host tissue. ‘ Ca. P. solani’ (strain SA-I, grapevine yellows) persisted in the host tissue despite the obvious recovery of the host plant and was always detected in the direct PCR. Conclusions: Both auxins induced recovery of phytoplasma-infected plants and affected tested ‘ Candidatus Phytoplasma’ species in the same manner, implying that the mechanism involved in phytoplasma elimination/survival is common to both, IAA and IBA. Significance and Impact of the Study: The results imply that in the case of some ‘ Candidatus Phytoplasma’ species, IBA-treatment could be used to eliminate phytoplasmas from in vitro grown Catharanthus roseus shoots.